The present invention relates to a liquid crystalline polyester and a method of producing the same.
Liquid crystalline polyesters having an aromatic ring skeleton are used recently in electric and electronic fields as materials excellent in heat resistance and tensile strength. Liquid crystalline polyesters are produced, for example, by a method of adding acetic anhydride to phenolic hydroxyl groups of an aromatic hydroxycarboxylic acid such as p-hydroxybenzoic acid and the like and/or an aromatic diol such as 4,4xe2x80x2-dihydroxybiphenyl and the like for acylation of the phenolic hydroxyl groups to give an acylated substance and trans-esterifying the acylated substance with an aromatic dicarboxylic acid such as terephthalic acid and the like, and other methods.
However, in this method, time required for acylation is long, leading to a problem in productivity, and there is further a problem that a liquid crystalline polyester having an aromatic skeleton obtained by this method has not necessarily sufficient impact strength though it has excellent heat resistance and tensile strength.
For solving such problems, there is known a method in which an organometal compound such as sodium acetate and the like is added as a catalyst in an acylation reaction to decrease the reaction time (JP-A No. 11-246654). However, this method has a problem that a metal ion remains in a resin, leading to poor insulation ability, and there is further a problem that a liquid crystalline polyester having an aromatic skeleton obtained by this method has not necessarily sufficient impact strength.
Further, there is also known a method in which an organic compound having low boiling point such as pyridine and the like is added as a catalyst in an acylation reaction to decrease the reaction time (JP-A No. 6-1836). However, this method has problems that time for trans-esterification is delayed and coloration owing to a side-reaction occurs and there is further a problem that a liquid crystalline polyester having an aromatic skeleton obtained by this method has not necessarily sufficient impact strength.
An object of the present invention is to provide a liquid crystalline polyester manifesting excellent impact strength without deteriorating excellent heat resistance and tensile strength, and a method for producing a liquid crystalline polyester having excellent productivity and causing no coloration.
The present inventors have intensively studied a liquid crystalline polyester which does not have the above-described problems, and resultantly found that a liquid crystalline polyester obtained by conducting acylation, trans-esterification, or the acylation and trans-esterification in the presence of a heterocyclic organic base compound containing two or more nitrogen atoms, manifests excellent impact strength while maintaining excellent heat resistance and tensile strength, and also that a liquid crystalline polyester can be produced efficiently without causing coloration due to a side reaction by conducting acylation, trans-esterification, or acylation and trans-esterification in the presence of a heterocyclic organic base compound containing two or more nitrogen atoms, and have completed the present invention.
Namely, the present invention provides
[1] a method for producing a liquid crystalline polyester comprising the steps of
acylating phenolic hydroxyl groups of an aromatic diol, an aromatic hydroxycarboxylic acid, or an aromatic diol and aromatic hydroxycarboxylic acid with a fatty anhydride to obtain an acylated substance, and
trans-esterifying said acylated substance with an aromatic dicarboxylic acid, an aromatic hydroxycarboxylic acid, or an aromatic dicarboxylic acid and aromatic hydroxycarboxylic acid,
wherein the acylation, the trans-esterification, or the acylation and trans-esterification is conducted in the presence of a heterocyclic organic base compound containing two or more nitrogen atoms, and
[2] a liquid crystalline polyester obtained by the method [1].
The liquid crystalline polyester of the present invention has an aromatic ring skeleton which forms a melted phase having optical anisotropy, is excellent in heat resistance and tensile strength, further, excellent also in impact strength.
The liquid crystalline polyester of the present invention can be obtained by polycondensation by trans-esterifying an aromatic dicarboxylic acid and/or an aromatic hydroxycarboxylic acid with an acylated substance obtained by acylating phenolic hydroxyl groups of an aromatic diol and/or an aromatic hydroxycarboxylic acid with a fatty anhydride, and is characterized in that it is obtained by conducting acylation, trans-esterification, or acylation and trans-esterification in the presence of a heterocyclic organic base compound containing two or more nitrogen atoms.
First, a process in which phenolic hydroxyl groups of an aromatic diol and/or an aromatic hydroxycarboxylic acid are acylated with a fatty anhydride will be described.
Examples of the aromatic diol include 4,4xe2x80x2-dihydroxybiphenyl (hereinafter, abbreviated as (C1) in some cases), hydroquinone (hereinafter, abbreviated as (C2) in some cases), resorcin (hereinafter, abbreviated as (C3) in some cases), methylhydroquinone, chlorohydroquinone, acetoxyhydroquinone, nitrohydroquinone, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene (hereinafter, abbreviated as (C4) in some cases), 2,7-dihydroxynaphthalene, 2,2-bis(4-hydroxyphenyl)propane (hereinafter, abbreviated as (C5) in some cases), 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, bis-(4-hydroxyphenyl)methane, bis-(4-hydroxy-3,5-dimethylphenyl)methane, bis-(4-hydroxy-3,5-dichlorophenyl)methane, bis-(4-hydroxy-3,5-dibromophenyl)methane, bis-(4-hydroxy-3-methylphenyl)methane, bis-(4-hydroxy-3-chlorophenyl)methane, 1,1-bis(4-hydroxyphenyl)cyclohexane,bis-(4-hydroxyphenyl) ketone,bis-(4-hydroxy-3,5-dimethylphenyl)ketone, bis-(4-hydroxy-3,5-dichlorophenyl)ketone, bis-(4-hydroxyphenyl)sulfide,bis-(4-hydroxyphenyl) sulfone (hereinafter, abbreviated as (C6) in some cases) and the like. These may be used singly or in combination of two or more.
Among them, 4,4xe2x80x2-dihydroxybiphenyl, hydroquinone, resorcin, 2,6-dihydroxynaphthalene, 2,2-bis(4-hydroxyphenyl)propane and bis-(4-hydroxyphenyl) sulfone are preferably used because of easy availability.
Examples of the aromatic hydroxycarboxylic acid include p-hydroxybenzoic acid (hereinafter, abbreviated as (A1) in some cases), m-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid (hereinafter, abbreviated as (A2) in some cases), 2-hydroxy-3-naphthoic acid,1-hydroxy-4-naphthoic acid, 4-hydroxy-4xe2x80x2-carboxydiphenyl ether, 2,6-dichloro-p-hydroxybenzoic acid, 2-chloro-p-hydroxybenzoic acid, 2,6-difluoro-p-hydroxybenzoic acid, 4-hydroxy-4xe2x80x2-biphenylcarboxylic acid and the like. These may be used alone or in combination of two or more. Of them, p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid are preferably used because of easy availability.
Examples of the fatty anhydride include, but are not limited to, acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, 2-ethylhexanoic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, xcex2-bromopropionic anhydride, and the like. These may be used in admixture of two or more. Acetic anhydride, propionic anhydride, butyric anhydride and isobutyric anhydride are preferably used from the standpoint of cost and handling property, and acetic anhydride is more preferably used.
The use amount of a fatty anhydride based on a phenolic hydroxyl group of an aromatic diol and/or an aromatic hydroxycarboxylic acid is preferably 1.0 to 1.2-fold equivalent.
The use amount is more preferably from 1.0 to 1.05-fold equivalent, further preferably from 1.03 to 1.05-fold equivalent from the standpoints of low out gas generation and solder blister-resistance and the like.
The use amount is preferably from 1.05 to 1.1-fold equivalent from the standpoint of impact strength.
When the use amount of a fatty anhydride is less than 1.0-fold equivalent based on the phenolic hydroxyl group, there is a tendency that equilibrium in an acylation reaction shifts to the fatty anhydride side and an unreacted aromatic diol or aromatic dicarboxylic acid is sublimated in polymerization into a polyester, causing clogging of the reaction system. Further, when over 1.2-fold equivalent, the resultant liquid crystalline polyester tends to be colored remarkably.
The acylation reaction is preferably conducted for 10 minutes to 30 hours at 130xc2x0 C. to 180xc2x0 C., and more preferably conducted for 20 minutes to 5 hours at 140xc2x0 C. to 160xc2x0 C.
Next, trans-esterification of an acylated substance with an aromatic dicarboxylic acid and/or an aromatic hydroxycarboxylic acid is described.
Examples of the aromatic dicarboxylic acid used in trans-esterification include terephthalic acid (hereinafter, abbreviated as (B1) in some cases), isophthalic acid (hereinafter, abbreviated as (B2) in some cases), 2,6-naphthalenedicarboxylic acid (hereinafter, abbreviated as (B3) in some cases), 1,5-naphthalenedicarboxylic acid, 4,4xe2x80x2-biphenyldicarboxylic acid, methylterephthalic acid, methylisophthalic acid, diphenyl ether-4,4xe2x80x2-dicarboxylic acid, diphenylsulfone-4,4xe2x80x2-dicarboxylic acid, diphenyl ketone-4,4xe2x80x2-dicarboxylic acid, 2,2xe2x80x2-diphenylpropane-4,4xe2x80x2-dicarboxylic acid and the like. These may be used alone or in combination of two or more. Of them, terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used because of easy availability.
As the aromatic hydroxycarboxylic acid used in trans-esterification, those as described above are listed.
The use amount of an aromatic dicarboxylic acid and/or an aromatic hydroxycarboxylic acid based on an acylated substance obtained by acylation of an aromatic diol and/or an aromatic hydroxycarboxylic acid with a fatty anhydride is preferably from 0.8 to 1.2-fold equivalent.
The trans-esterification (polycondensation) reaction is preferably conducted while raising the temperature at a rate of 0.1 to 50xc2x0 C./min. in the range from 130xc2x0 .C to 400xc2x0 C., and more preferably conducted while raising the temperature at a rate of 0.3 to 5xc2x0 C./min. in the range from 150xc2x0 C. to 350xc2x0 C.
In trans-esterifying an acylated fatty ester with a carboxylic acid, it is preferable to evaporate a by-produced fatty acid and an unreacted fatty anhydride, out of the system, for shifting the equilibrium.
Further, raw materials evaporating or sublimating with a fatty acid can be condensed or reverse-sublimated to be returned to a reactor by refluxing part of a fatty acid to be distilled and returning it to a reactor. In this case, they can be returned to a reactor together with a fatty acid even if they are not dissolved completely.
It is necessary to conduct acylation, trans-esterification, or acylation and trans-esterification in the presence of a heterocyclic organic base compound containing two or more nitrogen atoms.
Examples of the heterocyclic organic base compound containing two or more nitrogen atoms include an imidazole compound, triazole compound, dipyridilyl compound, phenanethroline compound, diazaphenanethrene compound, 1.5-diazabicyclo [4.3.0] non-5-ene, 1,4-diazabicyclo [2.2.2] octane, 1,8-diazabicyclo [5.4.0] unde-7-cene, N,N-dimethylaminopyridine and the like.
As the imidazole compound, imidazole compounds of the formula (I) are listed, for example. 
(wherein, R1 to R4 each independently represent a hydrogen atom, alkyl group having 1 to 4 carbon atoms, hydroxymethyl group, cyano group, cyanoalkyl group having 1 to 4 carbon atoms, cyanoalkoxy group having 1 to 4 carbon atoms, carboxyl group, amino group, aminoalkyl group having 1 to 4 carbon atoms, aminoalkoxy group having 1 to 4 carbon atoms, phenyl group, benzyl group, phenylpropyl group or formyl group.).
Examples of the imidazole compound include imidazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 4-ethylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole, 2,4-dimethylimidazole, 1-methyl-2-ethylimidazole, 1-methyl-4-ethylimidazole, 1-ethyl-2-methylimidazole, 1-ethyl-2-ethylimidazole, 1-ethyl-2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 4-cyanoethyl-2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole, 1-(cyanoethylaminoethyl)-2-methylimidazole, N-[2-(2-methyl-1-imidazolyl)ethyl]urea, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-methylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazole trimellitate, 1-cyanoethyl-2-ethyl-4-methylimidazole trimellitate, 1-cyanoethyl-2-undecylimidazole trimellitate, 2,4-diamino-6-[2xe2x80x2-methylimidazolyl-(1xe2x80x2)]-ethyl-S-triazine, 2,4-diamino-6-[2xe2x80x2-undecylimidazolyl(-(1xe2x80x2))-ethyl-S-triazin e], 2,4-diamino-6-[2-ethyl-4-methylimidazolyl-(1xe2x80x2)]-ethyl-S-tr iazine, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, N,Nxe2x80x2-bis(2-methyl-1-imidazolylethyl) urea, N,Nxe2x80x2-(2-methyl-1-imidazolylethyl)adipoamide, 2,4-dialkylimidazole-dithiocarboxylic acid, 1,3-benzyl-2-methylimidazolium chloride, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-cyanoethyl-2-phenyl-4,5-bis(cyanoethoxymethyl)imidazole, 2-methylimidazole.isocyanuric acid adduct, 2-phenylimidazole.isocyanuric acid adduct, 2,4-diamino-6-[2xe2x80x2-methylimidazolyl-(1xe2x80x2)]-ethyl-S-triazine .isocyanuric acid adduct, 2-alkyl-4-formylimidazole, 2,4-dialkyl-5-formylimidazole, 1-benzyl-2-phenylimidazole, imidazole-4-dithiocarboxylic acid, 2-methylimidazole-4-dithiocarboxylic acid, 2-undecylimidazole-4-dithiocarboxylic acid, 2-heptadecylimidazole-4-dithiocarboxylic acid, 2-phenylimidazole-4-dithiocarboxylic acid, 4-methylimidazole-5-dithiocarboxylic acid, 4-dimethylimidazole -5-dithiocarboxylic acid, 2-ethyl-4-methylimidazole-5-dithiocarboxylic acid, 2-undecyl-4-methylimidazole-5-dithiocarboxylic acid, 2-phenyl-4-methylimidazole-5-dithiocarboxylic acid, 1-aminoethyl-2-methylimidazole, 1-(cyanoethylaminoethyl)-2-methylimidazole, N-(2-methylimidazolyl-1-ethyl) urea, N,Nxe2x80x2-[2-methylimidazolyl(1)-ethyl]-adipoyldamide, 1-aminoethyl-2-ethylimidazole, 4-formylimidazole, 2-methyl-4-formylimidazole, 4-methyl-5-formylimidazole, 2-ethyl-4-methyl-5-formylimidazole, 2-phenyl-4-methyl-4-formylimidazole and the like.
As the triazole compound, for example, 1,2,4-triazole, 1,2,3-triazole, benzotriazole and the like are listed.
As the dipyridilyl compound, for example, 2,2xe2x80x2-dipyridilyl, 4,4xe2x80x2-dipyridilyl and the like are listed.
As the phenanethroline compound, for example, pyrimidine, purine, 1,7-phenanathroline, 1,10-phenanethroline and the like are listed.
As the diazaphenanethrene compound, for example, pyridazine, triazine, pyrazine, 1,8-diazaphenanethrene and the like are listed.
As the heterocyclic organic base compound containing two or more nitrogen atoms, imidazole compounds of the formula (I) are preferable from the standpoint of reactivity, and imidazole compounds of the formula (I) in which R1 represents an alkyl group having 1 to 4 carbon atoms and R2 to R4 represent a hydrogen atom are further preferable from the standpoint of hue, and 1-methylimidazole and 1-ethylimidazole are most preferable because of easy availability.
The addition amount of the heterocyclic organic base compound containing two or more nitrogen atoms based on 100 parts by weight of the total amount of an aromatic dicarboxylic acid, aromatic diol and aromatic hydroxycarboxylic acid used in raw material charging is preferably from 0.005 to 1 part by weight, and more preferably from 0.05 to 0.5 parts by weight from the standpoints of hue and productivity.
When the addition amount is less than 0.05 parts by weight, an effect of improving impact strength and the like tends to be small, and when over 1 part by weight, control of the reaction tends to be difficult.
It may be advantageous that the heterocyclic organic base compound containing two or more nitrogen atoms is present during one period in conducting acylation, trans-esterification, or acylation and trans-esterification, and the addition period is not particularly restricted, and may be directly before initiation of the reaction or during the reaction.
In particular, the shrinkage ratio of a molded article when molded can be reduced by adding a heterocyclic organic base compound containing two or more nitrogen atoms at 300xc2x0 C. or more in the trans-esterification.
For the purpose of increasing polymerization speed by accelerating a trans-esterification reaction, a small amount of catalyst may be added in an amount which does not lose the object of the present invention, if necessary. As the catalyst added, for example, germanium compounds such as germanium oxide and the like, tin compounds such as stannous oxalate, stannous acetate, dialkyltine oxide, diaryltin oxide and the like, titanium compounds such as titanium dioxide, titanium alkoxide, alkoxy titanium silicates and the like, antimony compounds such as antimony trioxide and the like, metal salts of organic acids such as sodium acetate, potassium acetate, calcium acetate, zinc acetate, ferrous acetate and the like, Lewis acids such as boron trifluoride, aluminum chloride and the like, amines, amides, inorganic acids such as hydrochloric acid, sulfuric acid and the like.
The acylation reaction and trans-esterification (polycondensation) reaction can be conducted, for example, using a batch-wise apparatus, continuous apparatus and the like.
The liquid crystalline polyester of the present invention obtained by the above-mentioned production method preferably contains repeating units of the following formula in an amount of at least 30 mol % from the standpoint of balance between heat resistance and impact resistance. 
As the liquid crystalline polyester of the present invention obtained by the above-mentioned production method, those having the following repeating structural units (a) to (f) are listed, for example.
(a): A combination of structural units based on the above-mentioned (A1) with structural units based on the above-mentioned (B2), or structural units based on a mixture of the above-mentioned (B1) and (B2) with structural units based on the above-mentioned (C3).
(b): A combination of (a) in which part or all of structural units based on the above-mentioned (C3) are substituted by structural units based on the above-mentioned (C1).
(c): A combination of (a) in which part or all of structural units based on the above-mentioned (C3) are substituted by structural units based on the above-mentioned (C2).
(d): A combination of (a) in which part or all of structural units based on the above-mentioned (C3) are substituted by structural units based on the above-mentioned (C4).
(e): A combination of (a) in which part or all of structural units based on the above-mentioned (C3) are substituted by structural units based on a mixture of the above-mentioned (C4) and (C5).
(f): A combination of (a) in which part or all of structural units based on the above-mentioned (A1) are substituted by structural units based on the above-mentioned (A2).
The weight-average molecular weight of the liquid crystalline polyester is preferably from 10000 to 50000, though it is not particularly restricted.
The liquid crystalline polyester of the present invention is excellent in heat resistance and tensile strength, further, excellent also in impact strength, therefore, it can be suitably used in highly heat-resistant materials typically including electric and electronic parts.